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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_EVEN..._PREPARE(3) sd_event_source_set_prepare SD_EVEN..._PREPARE(3)
sd_event_source_set_prepare - Set a preparation callback for event
sources
#include <systemd/sd-event.h>
int sd_event_source_set_prepare(sd_event_source *source,
sd_event_handler_t callback);
typedef int (*sd_event_handler_t)(sd_event_source *s,
void *userdata);
sd_event_source_set_prepare() may be used to set a preparation
callback for the event source object specified as source. The
callback function specified as callback will be invoked
immediately before the event loop goes to sleep to wait for
incoming events. It is invoked with the user data pointer passed
when the event source was created. The event source will be
disabled if the callback function returns a negative error code.
The callback function may be used to reconfigure the precise
events to wait for. If the callback parameter is passed as NULL
the callback function is reset.
Event source objects have no preparation callback associated when
they are first created with calls such as sd_event_add_io(3),
sd_event_add_time(3). Preparation callback functions are supported
for all event source types with the exception of those created
with sd_event_add_exit(3). Preparation callback functions are
dispatched in the order indicated by the event source's priority
field, as set with sd_event_source_set_priority(3). Preparation
callbacks of disabled event sources (see
sd_event_source_set_enabled(3)) are not invoked.
On success, sd_event_source_set_prepare() returns a non-negative
integer. On failure, it returns a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-EINVAL
source is not a valid pointer to an sd_event_source object.
-ESTALE
The event loop is already terminated.
-ENOMEM
Not enough memory.
-ECHILD
The event loop has been created in a different process,
library or module instance.
-EDOM
The specified event source has been created with
sd_event_add_exit(3).
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) from a parallel
thread. It is recommended to only do calls to setenv() from an
early phase of the program when no other threads have been
started.
sd_event_source_set_prepare() and sd_event_handler_t() were added
in version 229.
sd-event(3), sd_event_add_io(3), sd_event_add_time(3),
sd_event_add_signal(3), sd_event_add_child(3),
sd_event_add_inotify(3), sd_event_add_defer(3),
sd_event_source_set_enabled(3), sd_event_source_set_priority(3),
sd_event_source_set_userdata(3)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_EVEN..._PREPARE(3)
Pages that refer to this page: sd-event(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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